US3441493A - Electrolytic shaping apparatus - Google Patents

Description

April 29, 1969 L. A. WILLIAMS 3,441,493

ELECTROLYTIC SHAPING APPARATUS Original Filed Nov. 10, 1958 Sheet of 2 A. a. P0 W5? Sup/u Y INV EN TOR.

April 1969 v L. A. WILLIAMS 3,441,493

7 ELECTROLYTIC SHAPING APPARATUS Original Filed Nov. 10, 1958 Sheet of 2 73 i5 52 P F F V INVENTOR.

United States Patent Oifice 3,441,493 Patented Apr. 29, 1969 3,441,493 ELECTROLYTIC SHAPING APPARATUS Lynn A. Williams, Winnetka, Ill., assignor to Auocut Engineering Company, Chicago, 11]., a corporation of Illinois Original application Nov. 10, 1958, Ser. No. 772,960, new Patent No. 3,058,895, dated Oct. 16, 1962. Divided and this application July 25, 1966, Ser. No. 567,578

Int. Cl. B23p 1/04 11.8. Cl. 204-224 This application is a division of my application Ser. No. 158,042, filed Dec. 8, 1961, now US. Patent 3,276,987 entitled, Electrolytic Shaping Apparatus, which in turn is a division of my application Ser. No. 772,960, filed Nov. 10, 1958, entitled, Electrolytic Shaping, now issued into Patent No. 3,058,895, dated Oct. 16, 1962.

It has long been known that metal and metalloid materials may be removed by electrolytic attack in a configuration where the metal or metalloid workpiece is the anode in an electrolytic cell. This principle has been used industrially to some degrees for the removal of defective plating and the like, and is sometimes referred to as stripping. It has also been used to some extent for electrolytic polishing in which application, however, the principal purpose is to produce a smooth finish with a minimum removal of the work material. Here the purpose is to remove substantial amounts of metal rapidly and with accuracy.

In the present instance, the term metalloid is used somewhat specially in referring to those electrically conductive materials which act like metals when connected as an anode in an electrolytic cell, and are capable of being electrochemically eroded. The term as used here and in the claims includes metals and such similarly acting materials as tungsten carbide, for instance, and dis tinguished from such conductive nonmetalloids as carbon.

George F. Keeleric has proposed in his Patent No. 2,826,540, issued Mar. 11, 1958, for Method and Apparatus for Electrolytic Cutting, Shaping and Grinding, the use of electrolysis in conjunction with a metal bonded, abrasive bearing, moving electrode, and the method and apparatus of this Keeleric patent have found extensive industrial use.

The present invention departs from the teachings of Keeleric in utilizing relatively fixed or slow moving electrodes without abrasive, and is intended for work of a quite different character, as will appear in the detailed description of the invention which follows.

In general, in the present invention an electrode, quite frequently a hollow electrode, is advanced into the work material by mechanical means while electrolyte is pumped through the work gap between the electrode and the work, and at times the hollow portion of the electrode, under substantial pressure. In some circumstances the side walls of the electrode are protected by an insulating material so as to minimize removal of work material except where desired. Various forms of electrodes are used for different kinds of work, and likewise ditferent technique of advancing the electrode toward and into the work material are used, depending upon the nature of the operation to be performed. An important aspect of the invention lies in providing electrodes in which a flow of electrolyte between the electrode and the work is maintained at high velocity and across a short path between the point of entry and the area of exit regardless of the overall size of the electrode. An electric current is supplied so that current passes from the electrode, which is negative, through the electrolyte to the workpiece, which is positive. For purposes of shaping the electrodes, direct current may be passed in the opposite sense to make the electrode ositive. In some instances, alternating current may be used.

2 Claims Among the objects of the invention are the following:

To provide novel apparatus for rap-id removal of work material by electrolytic means;

To provide novel apparatus for imparting desired shapes and contours to a workpiece by electrolytic action; and

To provide novel apparatus using an alternating current source for the electrolyzing current with a rectifying element at the work gap.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of one form of electrolytic shaping apparatus embodying the present invention;

FIG. 2 is a diagrammatic representation of an electrolyte supply system which forms a portion of the apparatus of FIG. 1; and

FIG. 3 is a longitudinal sectional view of a form of electrode connected for use with alternating current.

Referring to FIG. 1, the apparatus of this invention includes a frame member 1 which in this instance is the frame member of a conventional and well known arbor press sold under the trade name of Famco. It includes a base section 3, a column 5, and a head 7 which is adapted in the conventional manner to accommodate a ram 9 for vertical reciprocating motion. The detail of the ram mounting is not important to this invention, but it is desirable to provide adjustable gibs or the equivalent in the head so that the ram may move vertically with a smooth action and without lateral play which might introduce undesired side motion. To the bottom of the ram 9 there is mounted a workplate 11, made of an electrically insulating material which is resistant to the corrosive effect of the electrolyte and through which a plurality of bolt holes is provided to permit adjustable mounting of a work holding vise 15.

On the base portion 3 there is mounted a metal bottom plate and on top of this a waterproof chemical resistant plastic mounting plate 19. This is provided with a number of threaded bolt holes to permit mounting of an electrode holder 21, which is made of suitable metal and is provided with one or more mounting slots so that it can be adjusted as to its position by selection of the suitable bolt holes in mounting plate 19.

At the working end, the electrode support member 21 is hollow and is adapted to receive an electrolyte feed tube fitting 27 connected to a line leading to a source of electrolyte under pressure.

Extending from the upper surface there is mounted an electrode 31, having a conductive working face, shown here as fastened by brazing to a pipe nipple threaded into the electrode support member 21. Within the hollow support member 21 the electrode is connected by a suitable passage to the feed tube fitting 27.

An electric cable 34 is connected to the electrode block or support member 21 and supplies current from the power source. Another electric cable 35 is fastened to work plate 11 to furnish the other (normally positive) connection from the power source.

To move the workplate 11 up and down, a lead screw 37 is secured to and extends upwardly from the upper end of the ram 9. A lead nut 39 is threaded upon the lead screw and is mounted between two horizontal plates 41 which are supported by four column bars 43. The lead nut peripherally is formed as a worm gear so that it may be rotated to move the lead screw 37 up and down. A journal plate 45 is mounted to the plates 41 and carries a bearing bushing 47 which supports the outboard end of a drive shaft 49 which carries worm 51 meshed with the peripheral worm gear of lead nut 39'.

The worm drive shaft 49 is, in turn, rotated by a variable speed electric motor drive 53- mounted upon a platform 55 attached to the column 5. This drive mechanism has a speed adjusting handle 57 and a reversing handle 59, the latter having a neutral midposition as well as updrive and downdrive positions.

The sizes and proportions of the drive parts are arranged to permit adjustment in the vertical speed of movement of the workplate 11 from zero to one inch per minute. The motion must be smooth, not jerky, and accordingly reasonable accuracy and freedom from excessive friction are an advantage in the moving drive parts. The lead screw 37 may be protected against splatter and corrosion by a plastic enclosure 61 wrapped around the column bars 43.

A conventional dial indicator 63 is shown as mounted to the head 7 of column and has its working tip extended downwardly against the upper surface of workplate 11, so as to indicate relative movement as between these elements.

The entire assembly is mounted in a pan 65 which has an outlet spud adapted to drain electrolyte back into a supply sump or reservoir 74. The work plate 11 is fitted with plastic curtains 71 which can be tucked down below the level of the pan top to prevent excessive splatter, and to enclose the work area for the workpiece and the electrode 31.

The plumbing system (FIG. 2) comprises a low pressure pump 73 which feeds a suitable conductive electrolyte from the reservoir 74 through a filter 75 into high pressure pump 77, the outlet of which leads to a bypass valve 79 which may be either manually set or of the spring loaded constant pressure type. On the inlet side of the bypass valve 79 a pressure gauge 81 is mounted. Also from the inlet side, a pipe lead is taken through a needle valve 83 to an electrolyte feed tube 84 leading to the electrode fitting 27. A second gauge 29 is connected to the feed tube 84 so as to indicate the pressure at the electrode.

In operation, a workpiece is positioned in the vise 15 above the electrode 31, and the work plate 11 is then driven down until the workpiece is almost touching electrode 31 as gauged by a piece of paper or shim of known thickness, say .003 inch. The dial indicator 63 is then adjusted to zero minus the known thickness, .003 inch in this example. The curtains 71 are lowered or otherwise closed, the electrolyte pumps 73 and 77 are started, and the valves 79 and 83 are adjusted so that gauge 81 reads about 120 p.s.i., and gauge 29 about 90 p.s.i. This is done while the reversing handle 59 is in neutral position. Then, simultaneously, the reversing handle is moved to down drive position, and the electric power supply is turned on.

As the electrode approaches the workpiece, there will be a rise in pressure at the gauge 29'. If the capacity of pumps 73 and 77 is several times the free flow discharge rate through the electrode, the pressure upstream of the needle valve 83 and of bypass valve 79' as read at gauge 81 will change scarcely at all with changes in proximity of the electrode 31 to the work, for most of the flow is passing through bypass valve 79, and it is the adjustment of this which is principally determinative of the pressure at gauge 81. In short, the pumps and pumping system up to the needle valve 83 constitute a substantially constant pressure source. The same result may be obtained in many other ways. A constant pressure type pump may be used; e.g., a centrifugal pump operating near cutoff. Or a pressure regulator may be used. Or a spring-loaded relief valve adapted to maintain constant pressure may be used.

Needle valve '83, however, is set so as to constitute a sufficient restriction to flow so that when the electrode is discharging into the open, the pressure, as read at gauge 29, will be noticeably lower than when its outlet is restricted by being in close proximity to the work.

Thus, if gauge 81 normally reads 120 p.s.i., then when the electrode 31 touches the workpiece so as to shut off the flow, or nearly so, the pressure downstream of needle valve 83 as read at gauge 29' will rise to almost the same value, 120 p.s.i. If, however, the electrode 31 is spaced away by several thousandths of an inch, the pressure at gauge 29 will drop, say to p.s.i.

This change in liquid pressure may be used in adjusting the rate of feed of the work toward the electrode.

The initial feed rate may be set at a low level (for an unknown working condition or work material), and then increased by adjustment of the handle 57. Gauge 29 is observed to watch for a pressure rise which approaches that of gauge 81. It takes a little time for the pressure reading to stabilize during actual removal operations, for inasmuch as material is being removed by anodic dissolution, it is necessary for the moving electrode to catch up with the receding work material and to establish an equilibrium spacing distance, for as the electrode comes closer to the work, the removal rate tends to increase. By the exercise of reasonable care, it is possible to make a precise adjustment such that the electrode pressure gauge 29 reads only a few pounds per square inch lower than gauge '81, indicating that the electrode is moving forward at such a rate as to leave only a small gap between the electrode and the work.

In effect, this hydraulic system constitutes a flow meter, and the same result may be obtained by using a more formal flow meter to sense the flow rate through the gap between the electrode and work. Such flow meter may be of any suitable sort, as for instance of the orifice type (which, in effect, uses the principle of the system just described), or of some other type, for example, that in which a moving bob is supported by upward flow in a conical glass vessel (e.g., the Fischer & Porter type).

It is not easy to measure this gap with accuracy, as apparently it is not always uniform at every point, but as measured in a practical way, by turning off the current and advancing the electrode until it seems to bottom, the distance may be as small as .001 inch or less, to as much as .010 inch, with satisfactory results, although it is preferred to work with the shortest spacing distance which can be managed without causing occasional contact and arcing between the electrode and the work, and I have found that about .002 inch to .005 inch is usually a safe distance while still permitting rapid removal of work material.

In general, low voltages and close spacing, of the order of .001 inch to .005 inch, give high removal rates and low electric power costs and a higher degree of accuracy, but less striation is produced upon the side wall of the work cavity when greater spacing, of the order of .010 inch, is used. The greater spacing results in a lower work removal rate unless the voltage is raised, however, since removal rate is a function of current. As a practical matter in most applications, I prefer to use about 4 to 15 volts and from to 3,000 amperes per square inch of active electrode area.

It should be noted that work material is removed by electrolytic action, not by spark or are erosion as with the so called electrodischarge method. This is important for several reasons, among them the fact that damaging thermal metallurgical elfects on the work material are avoided and that there is virtually no erosion of the electrode.

As taught in Patent No. 3,058,895, suitable controls are provided to regulate the rate of feed of the electrode 31 and the workpiece relatively toward each other.

FIG. 3 shows in detail the electrode of the present invention. The tip 297 is made of tantalum, and is fastened by welding, brazing, or swaging to the electrode body 275, which may be made of any suitable less costly material, such as copper or cold rolled steel. The special utility of the tantalum tip is that it permits the use of an alternating current electrical supply system, readily and cheaply available without rectification. All that is needed is simple stepdown transformer. If an acidic electrolyte is used,

the tantalum will pass current when it is a cathode but not when it is an anode Thus, current will pass in a direction suitable for removing work material but will not pass in a direction to attack the electrode.

The inner and outer walls of the body 275 are coated with ceramic 283 or other insulating material so that they will not be attacked by reverse electrolytic action.

The tantalum electrode permits a very inexpensive apparatus, although since it works only on the half cycle, its removal rate is not as great as that of the direct current system. However, where a large number of cavities is to be made simultaneously, a plurality of tantalum tipped electrodes may be used, and where the workpieces are separate, the alternating current electrical connections are so made that half of the electrolytic work cells are connected in one sense and the other half in the reverse sense, so that both halves of the alternating current cycle are substantially equally loaded.

From the foregoing it will be appreciated that the objectives which were claimed for the invention at the outset of the description are fully attained by the apparatus shown and described.

Also from the foregoing description of my invention it will be appreciated that many changes may be made in the apparatus without departing from the scope or spirit of the invention, and that the scope of the invention is to be determined from the scope of the accompanying claims.

I claim:

1. In an electrolytic apparatus for removing material from an electrically conductive and electrochemically eroded workpiece by means of an electrode having a conductive working end, means for relatively moving said electrode and the workpiece toward each other to define a work gap therebetween, means for pumping an electrolyte to and through the work gap, the working end of said electrode being formed of a material having a rectifying action such that when current flows the electrode will be cathodic, and circuit means for impressing an alternating electric potential between the electrode and the workpiece.

2. Apparatus as claimed in claim 1, wherein the material having a rectifying action is comprised of tantalum.

References Cited UNITED STATES PATENTS 3,038,849 6/1962 Preiser 204-290 XR HOWARD S. WILLIAMS, Primary Examiner.

DONALD R. VALENTINE, Assistant Examiner.

US. Cl. X.R.

Dedication 3,441,493.Lymz A. Williams, Winnetka, I11. ELECTROLYTIC SHAPING APPARATUS. Patent dated Apr. 29, 1969. Dedication filed Dec. 23, 1971, by the assignee, Anoout Engineering Company. Hereby dedicates to the Public the portion of the term of the patent subsequent to Dec. 24, 1971.

[Ofiicial Gazette April 25, 1972.]

Claims (1)

1. IN A ELECTROLYTIC APPARATUS FOR REMOVING MATERIAL FROM AN ELECTRICALLY CONDUCTIVE AND ELECTROCHEMICALLY ERODED WORKPIECE BY MEANS OF AN ELECTRODE HAVING A CONDUCTIVE WORKING END, MEANS FOR RELATIVELY MOVING SAID ELECTRODE AND WORKPIECE TOWARD EACH OTHER TO DEFINE A WORK GAP THEREBETWEEN, MEANS FOR PUMPING AN ELECTROLYTE TO AND THROUGH THE WORK GAP, THE WORKING END OF SAID ELECTRODE BEING FORMED OF A MATERIAL HAVING A RECTIFYING ACTION SUCH THAT WHEN CURRENT FLOWS THE ELECTRODE WILL BE CATHODIC, AND CIRCUIT MEANS FOR IMPRESSING

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